The use of bar code symbols to encode identification parameters for a variety of items has become commonplace. Bar code symbols are used, for example, to encode product identification and price information for consumer goods, part numbers and manufacturing lot numbers for machine parts, and identification codes for documents. The bar code symbols are usually attached to the item to be encoded through the use of a preprinted label, directly printed on the item itself, or printed on material used to package the item.
The variety of printing methods utilized to generate the bar code symbols, for example dot-matrix, ink-jet or offset printing, can cause a problem for equipment designed to read or decode the symbols. Different printing techniques can cause differences in optical characteristics, such as the reflectance, as well as physical characteristics, such as the width, of the elements of the printed bar code symbols. The same printing method can also yield various quality results due to variables associated with the printing process. Thus, two printed symbols that appear identical to the human eye may not be similarly interpreted by equipment designed to decode the symbols, i.e., the decoding equipment may be able to properly interpret the first bar code symbol but may not be able to interpret the second bar code symbol as a result of the above-described differences.
Standards have been developed to insure that bar code symbols are printed to exhibit uniform characteristics when decoded. ANSI Specification "Bar Code Print Quality" X3.182-1990, for example, defines a method of grading the quality of printed bar code symbols. In theory, a bar code symbol printed to a specific standard should be capable of being universally read by different decoding devices designed to decode bar code symbols printed to the standard. In practice, however, the inability to monitor the quality of the bar codes symbols on-line, i.e. as they are being read by the decoding apparatus, causes difficulties when one is trying to evaluate whether a decoding error was caused by a poor quality bar code symbol or by a decoding equipment malfunction.
Traditionally, a stand alone dedicated bar code verifiers, such as the QUICK CHECK 5 manufactured by Photographic Sciences Corporation of Webster, New York or the INSPECTOR II manufactured by RJS Inc. of Monrovia, California, have been employed to verify the quality of a bar code symbol when the decoding apparatus indicates that the bar code symbol is unreadable or unrecognizable. The dedicated bar code verifier, however, may utilize a different analysis methodology and decoding process--including different illumination wavelengths and measuring apertures--than the decoding apparatus being employed to read the bar code symbol. Thus, the data produced by the dedicated bar code verifier may not correspond to the data produced by the decoding apparatus which causes further difficulties when attempting to isolate the source of a decoding error, namely, one is faced with finding a way to correlate the data produced by the bar code verifier with the data produced by the decoding apparatus and resolving any differences.
The problems associated with the mismatch in processing techniques and hardware between the decoding apparatus and a stand alone bar code verifier is further exasperated when a marginal quality bar code symbol is under evaluation. The decoding apparatus may reject the marginal bar code symbol, for example, while the stand alone bar code verifier may accept the marginal bar code symbol or the reverse situation may occur. An operator may then decide to analyze a sample "known good" bar code symbol to determine whether the decoding apparatus or the stand alone verifier is providing correct data. Both devices, however, may indicate that the sample bar code symbol is acceptable. The operator is then left in a quandary, unable to determine which device is accurately representing the quality of the bar code symbol. This situation can cause a great deal of frustration for the operator who cannot determine whether the bar code symbol printing quality or a decoding equipment malfunction is causing the decoding errors.
In view of the above, it would be desirable to provide a method and apparatus that is capable of evaluating the quality of bar code symbols on-line, i.e. as the symbols are decoded, thereby avoiding the problems associated with the use of a stand alone bar code verifiers.